Choke actuating mechanism



Dec. 19, 1961 l.. c. DERMOND ET Al. 3,013,544

CI-IOKE ACTUATING MECHANISM Filed NOV. 18, 1960 il J? ZZ ATTORNEY United States Patent Office 3,013,544 CHOKE ACTUATING MECHANISM Lawrence C. Dermond and Norman G. Bruinsma,

Rochester, N.Y., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Nov. 18, 1960Ser. No. 70,294 6 Claims. (Cl. 12S-119) The present invention relates to an actuating mechanism in which a carburetor choke valve is moved toward a partially closed position during accelerating or high load operating conditions when the engine is only partially warm. More specifically, the present invention is an improvement over copending application Serial No. 754,841, Braun, led August 13, 1958, and now Patent No. 2,969,783, granted Jan. 31, 1961.

ln order to improve the economy of carburetor operation, it has been found that, except for certain limited operating conditions, it is possible to take-off or open a choke valve more rapidly than has been done in the past. The result of rapid choke valve come-olf is a leaner and more economical fuel-air mixture. However, it is not enough to simply set an auto-matic choke operating mechanism for leaner operation, which can be done with current automatic chokes, since there are certain operating conditions under which a partially warmed engine will not function properly on a lean mixture when overloaded. In other words, shortly after an engine has been started and during steady-state operation, e.g. one in which the engine is only lightly or gradually loaded, it is possible to open the choke valve and operate ona relatively lean mixture. However, with the engine only partially warmed and the choke essentially opened, a sudden loading of the engine, as occurs during accelerating conditions, will cause the engine to falter due to atoo lean fuel-air mixture.

In the present invention a choke controlling mechanism is provided in which the choke is adapted to open and rapidly lean out the fuel-air mixture shortly after starting to increase fuel economy'under conditions which have in the past used excessive quantities of fuel to cover a few operating contingencies. However, in addition the present choke actuating mechanism includes a device which is adapted to automatically return the choke to ya partially closed position when a partially warmed engine is suddenly heavily loaded. In this way the fuel-air mixture is momentarily enriched to accommodate the increased engine load and the engine will continue to function smoothly. 'Upon a diminution in the engine loa'd or'upon complete warming of the engine, the choke valve will assume its fully open position in which the carburetor `will function most economically.

The present choke actuating mechanism is an improvement over the aforenoted copending Braun application in providing a greatly simplified mechanism which has been' developed to achieve the aforenoted operation and as a consequence of which simplification the Vcommercial utili- Zation of such a device is greatly enhanced.

In general, the choke valve under consideration is controlled by three distinct forces. First, the choke valve is of the unbalanced `type such that it tendsvto move in an opening direction in accordance, with air-flow through the carburetor induction passage. Second, through a suitable linkage mechanism, the opening movement of the choke valve is resisted by ya thermostator bimetal member when the engine is cold or only partially warmed. Finally, the chokegclosing operation of the thermostat is adapted to be modified by a manifold vacuum responsive device which partially opens the choke valve against the force of the thermostat when the engine becomes operative. It is this latter manifold vacuum responsive mechanism that has been uniquely redesigned to not only permit the choke valve to be slightly opened as soon as the engine becomes operative, but which also permits the choke va-lve to be returned to a partially closed position when a partially warmed engine is suddenly over loaded as by moving the throttle valve to a fully open position.

The present manifold vacuum device includes a diaphragm member operatively interconnected with the thermostat and choke valve in a unique manner which permits the diaphragm to both open and close the choke valve depending on the needs of the engine. More specifically, the diaphragm divides a casing into a pair of chambers one of which openly communicates with a source of manifold vacuum and the other of which communicates with said vacuum source through a unique orifice-valve arrangement which is part of the means for interconnecting the diaphragm with the choke actuating mechanism. The orifice and valve arrangement is such that pressure differentials are created across the diaphragm which cause the latter to be moved in one direction under certain operating conditions to partially open the choke valve and which differential may be reversed to move the diaphragm in the opposite direction and thereby move the choke valve to a partially closed position.

The details as well as other objects and advantages of the present invention will be apparent from a perusal of the detailed description which follows.

In the drawings:

FIGURE l shows a carburetor embodying the subject invention; and

FIGURES 2, 3 and 4 show the cho-ke actuating mecha-` nism in various operating positions.

valve is articulated in any well known manner to an accelerator pedal mounted in the passenger compartment.

A choke valve 18 is also rotatably mounted within induction passage 12 and is adapted to restrict the quantity of air-flow through the induction passage during engine warming operation to provide an enriched fuel-air mixture. Choke valve 18 is mounted on a shaft 20 which is offset in relation to the induction passage to provide an unbalanced valve adapted to be opened by air-flow through the induction passage. f

rl'lie operation of choke valve 18 is controlled by an automatic choke device indicated generally at 22.v Automatic choke device 22 includes a coiled thermostat or v bimetal element 24 fixed at one end to a shaft 26. vThe other end of bimetal element 24 is formed as an elongated loop 27 the ends of which engage an arm 28 of lever 30. Lever 30 is fixed to a shaft 32 which is rotatably supported in automatic choke casing `34. A link 36` is also xed to shaft 32 and is adapted to rotate as the shaft and lever 30 are rotated. A second link 38 is fixed to choke shaft 20 for rotation therewith. A third or intermediate link 40 is articulated between links 36 and 38 whereby rotation of` automatic choke lever 30 will impart a corresponding ing 42 to which a iirst servo casing member 44 is secured andwhich casing coacts with-anothercasing member 46 toperipherally. clamp a flexible diaphragm 48 therebe-` tween. A valve housing member 50 is centrally securedl to .diaphragm T48. Housing 50 includes a central opening therethrough comprised of counterbored portions 5'2 andV Y 54 and opening 56. A r-od 58 having a ball end '60 disposed in counterbored portion 54 of housing 50 also ex- Patented Dec. 19, 1961 tends through opening 56 and is connected at its other end to an arcuate slot 62 formed in lever 30. For reasons which will be subsequently more apparent, ball end 60 coacts with housing opening 56 to provide a valve device.

A dished orifice plate member 64 is pressed within counterbore 52 and includes a restricted opening or orifice 66. While it may be varied in size in accordance with the operating characteristics of a particular engine, orice 66 is approximately .018 inch in diameter in the illustrated device.

A bifurcated stop member 68 is also secured to housing 50 and is adapted to coact with casing 46 to limit the rightward or choke closing movement of diaphragm 48.

An atmospheric vent member 70 is centrally disposed in casing 46 and also includes an opening within which an orifice plate 72 is disposed. An orifice 74 is formed in plate 72 and, for illustrative purposes, is approximately .012 inch in diameter. A filter element 76 is disposed in an enlarged portion of member 70 for the purpose of preventing impurities from entering casing 46.

Automatic choke casing 34 communicates through a port 78 and a passage or conduit 80 with intake manifold 14. Casing chamber 82 communicates with diaphragm chamber 84 which in turn communicates through valve housing Si) with the second diaphragm chamber 86. Diaphragm chamber 86 is bled to the atmosphere through orifice 74. The operative relationships between the various parts described will now be made clear in considering the operation of the subject choke actuating mechanism.

Referring to FIGURE l, choke valve 18 is shown in a closed position and the remaining elements are in the position which represents the engine being shut off and cold. In this instance there is no manifold vacuum acting on either side of diaphragm 48 and thermostat 24 acts through lever and links 36, 38 and 40 to maintain the choke valve in a closed position.

FIGURE 2 is representative of the position of the choke controlling components immediately after the engine has been started and while the same is still cold. In this instance, manifold vacuum is admitted to automattic choke casing chamber 82 and in turn communicates with diaphragm chamber 84 urging the diaphragm to the left until the diaphragm abuts against easing 44. The leftward movement of diaphragm 48 moves rod 58 to the left which urges lever 30 through a limited amount of clockwise movement. This movement of lever 30 causes links 36, 3S and 4i) to rotate choke valve to a partially opened position as indicated. This cracking or slight opening of the choke valve is necessary after the engine has been started in order that the rich starting mixture be leaned somewhat in order to maintain the engine operative.

This leftward movement of diaphragm 48 causes relative movement between valve casing 50 and rod 58 permitting ball member 60 to uncover housing opening 56. in this way manifold vacuum in chamber 84 is communicated through orifice 66 to diaphragm chamber 86. In view-of the restricted bleeding of chamber 86 to atmosphere through orifice 74, the manifold vacuum in the chamber will be somewhat less than that acting on diaphragm chamber 84 an hence the diaphragm will be maintained in its leftward position during normal engine operation.

Next, assuming the engine is still not fully warmed and further that the operator suddenly loads the engine as by opening the throttle valve, manifold vacuum will drop perceptibly andl approach atmospheric pressure in chambers S2 and 84. ln view of the fact that communication between diaphragm chambers 84 and 86 is restricted by orifice 66, the manifold vacuum in chamber 86 will not be dissipated as quickly as that in chamber 84 as a consequence of which diaphragm 48 will be moved toV the right until stop member 68 abuts against casing 46. The rightward movement of the diaphragm will in turn impart a counterclockwise rotation'to lever 30 which causes links 36, 38 and 40 to move the choke valve from a substantially fully open position, as sh-own on dotted lines in FIGURE 3, to a partially closed position and thereby provide suitable enrichment of the fuel-air ratio which prevents stumbling of the partially warm engine.

As the engine progresses from the partially warm condition of FIGURE 3 to a fully warmed position in FIG- URE 4, thermostat 24 will continue to unwind in a clock wisc direction until the left end of the thermostat loop 27 engages leg 28 of lever 30 and places rod 58 under tension. In this event, ball member 60 will seat against ball housing opening 56 and block flow therethrough. Under these conditions manifold vacuum cannot be communicated to diaphragm chamber 86 which is, therefore, gradually bled down to atmospheric pressure through orifice 74. Hence, a sudden drop in manifold vacuum, after the engine is fully warm, will occasion no further movement of diaphragm 48 and choke valve 18 is, therefore, no longer affected -by the diaphragm until such time as the engine has once again cooled.

We claim:

l. A charge forming device for an internal combustion engine comprising an induction passage for supplying a fuel-air mixture to the engine, a throttle valve disposed in said induction passage for controlling the quantity of said mixture, a choke valve disposed in said induction passage for varying the richness of said mixture by restricting air flow through said induction passage, a choke controlling device comprising a first casing, a lever pivotally mounted on said casing, linkage means interconnecting said lever and said choke valve, a temperature responsive member adapted to engage said lever and urge said lever in a choke valve closing direction with a force inversely proportional to engine temperature, said casing including a chamber within which said temperature responsive member is disposed, conduit means communicating said chamber with a source of manifold vacuum, a fiexible diaphragm associated with said casing and including one side communicating with said chamber and the other side communicating with a second chamber, means associated with said diaphragm providing a restricted connection between said first and second chambers, a rod interconnecting said diaphragm and said lever whereby movement of said diaphragm is adapted to impart movement to said lever, said rod including a portion adapted to coact with said means to prevent communication between said first and second chambers permitting a pressure differential to exist across said diaphragm, and an orifice providing a restricted atmospheric bleed into said second chamber.

2. A charge forming device for an internal combustion engine comprising an induction passage for supplying a fuel-air mixture to the engine, a throttle valve disposed in said induction passage for controlling the quantity of said mixture, a choke valve disposed in said induction passage for varying the richness of said mixture by restricting air flow through said induction passage, a choke controlling device comprising a first casing, a lever pivotally mounted on said casing, linkage means interconnecting said lever and said choke valve, a temperature responsive member adapted to engage said lever and urge said lever in a choke valve closing direction with a force inversely proportional to engine temperature, said casing including a chamber within which said temperature responsive member is disposed, conduit means communicating said chamber with a source of manifold vacuum, a flexible diaphragm associated with said casing and including one side communicating with said chamber and the other side communicating with a second chamber, an open ended cylinder centrally mounted through and communicating said first and second chambers, said cylinder including small and large diameter bore portions extending longitudinally thereof, a rod connected at one end to said lever and the other end extending through the small diameter portion of said cylinder, said other end of therod terminating in an enlarged portion, a plate having an orifice therein disposed within the large bore portion of the cylinder, said plate and said small bore portion of the cylinder contining the enlarged rod portion therebetween so as to permit limited axial movement between the rod and cylinder whereby the enlarged rod portion coacts with the small bore portion of the cylinder to control tlow between said chambers, and an orifice providing a restricted atmospheric bleed into said second chamber.

3. A carburetor choke valve operating device for an internal combustion engine comprising first and second casing members, a flexible diaphragm peripherally clamped between said members, iirst and second chambers respectively formed by the diaphragm and said casing members, linkage means interconnecting said diaphragm and the choke valve, a temperature responsive element operatively connected to the linkage means and adapted therethrough to move the choke valve in a closed direction with a force inversely proportional to temperature, a conduit connecting said first chamber with a source of manifold vacuum, first orifice means communicating the first and second chambers, and second orifice means providing a restricted atmospheric bleed into the second chamber, said linkage means being adapted to block flow through the first orifice means.

4. A carburetor choke valve operating device as set forth in claim 3 in which the linkage means includes a rod having a ball end adapted to coact with the first orifice means to control fiow between the first and second chambers.

5. A carburetor choke valve operating device as set forth in claim 4 in which the first orifice means comprises a housing member centrally mounted upon said diaphragm, said housing including an opening therethrough communicating the first and second chambers, an orifice plate disposed in the housing opening, the ball end of said rod coacting with said housing opening to control iiow between said chambers.

6. A carburetor choke valve operating device as set forth in claim 5 in which the housing opening includes a small diameter portion through which said rod extends, and an enlarged diameter' portion adapted to receive the ball end of the rod, said orifice plate being mounted in said enlarged diameter portion to permit limited movement of said ball end relative to said small diameter portion.

No references cited. 

